This invention relates to a digital cellular radio telephone system such as a portable telephone system, and more particularly to an electric field detecting method.
A system is known as a cellular radio telephone system in the art in which, in order for a mobile unit to detect a net work, a broadcasting channel transmitted from a base station does not perform a continuous signal transmission, but performs a repetitive burst signal transmission with a predetermined period. In the system, the mobile unit detects the channel is as follows:
FIG. 2 shows an example of the system in which a base station repetitively performs a broadcasting channel burst transmission. In the system, for the same period of time as the burst transmission repetitive period (T), the mobile unit performs a signal receiving operation, thus receiving a broadcasting channel as much as one burst. This is carried out for each of the broadcasting channel prospective frequencies. Usually, the strongest electric field is selected as a broadcasting channel to be received.
However, the above-described conventional method suffers from the following problem: In the case where there are many broadcasting prospective frequencies, or the period of the broadcasting channel burst transmission is long, the signal reception of all the prospective frequencies takes a long period of time.
Accordingly, an object of this invention is to provide an electric field detecting method in which, even if the number of broadcasting prospective frequencies are large or the period of the broadcasting channel burst transmission is long, the period of time required for receiving all the prospective frequencies is shortened.
In order to achieve the foregoing object of the invention, in a broadcasting channel receiving system of cellular radio telephone system, according to the invention, a processor is provided which controls the timing of transmitting control data to a frequency synthesizer and the timing of controlling a signal receiver, and a plurality of frequencies are repeatedly received for every period of time which is shorter than a period of time for which a base station transmits a burst at predetermined time intervals.
Hence, as many receiving fields as the number of repetitive frequencies can be detected at the same time. This feature decreases a period of time required for receiving all the prospective frequencies.
More specifically, according to first aspect of the invention, it is provided an electric field detecting method in which, in detecting a broadcasting channel which is transmitted every predetermined period of time, measurement of receiving electric fields of a plurality of frequencies is repeated for a period of time which is shorter than a period of time of a burst transmission which is carried out by a base station, thereby to decrease a broadcasting channel detecting time. That is, the method has a function of decreasing the broadcasting channel detecting time.
According to the second aspect of the invention, in the electric field detecting method, the period of repetition of the measurement of the receiving electric fields of the plurality of frequencies is made equal to the period of time of the burst transmission which is carried out by the base station, thereby to maximize a receiving electric field measurement efficiency with a limitation that no broadcasting channel detection leakage occurs. That is, the method has a function of maximizing the receiving electric field measurement efficiency to with a limitation that no broadcasting channel detection leakage occurs.
According to the third aspect of the invention, in the electric field detecting method, in the case where the burst position of a broadcasting channel occurs at the middle of a detection period-of-time, in order to prevent a broadcasting channel detection leakage, signal reception data are stored in memory until reception of the following same frequency, and a receiving electric field detection is carried out in combination with reception of the following same frequency. That is, the method has a function of preventing the broadcasting channel detection leakage in the case where the burst position of the broadcasting channel occurs at the middle of the detection period-of-time.
According to the fourth aspect of the invention, in the electric field detecting method, in the case where the burst position of a broadcasting position occurs at the middle of a detection period-of-time, in order to prevent a broadcasting channel detection leakage, and to reduce the consumption of memory, the number of frequencies for repetition of a receiving electric field measurement is set to a value which is obtained by subtracting one from the maximum number that one cycle does not exceed the burst transmission period-of-time. That is, the method has a function of preventing the broadcasting channel detection leakage, and reducing the consumption of memory.
According to the fifth aspect of the invention, the electric field detecting method in which, after a broadcasting channel transmission burst is detected with a frequency, the approximate position of the transmission burst is estimated, and, only during that period, a signal receiving operation is carried out, whereby the signal receiver is decreased in operation ratio. That is, the method has a function of decreasing the operation ratio of the signal receiver.
According to the present invention, it is provided a broadcasting channel receiving system of cellular radio telephone system, in which a processor is provided which controls the timing of transmitting control data to a frequency synthesizer, and the timing of controlling a signal receiver, and a plurality of frequencies are repeatedly received for every period of time which is shorter than a period of time for which a base station transmits a burst at predetermined time intervals. That is, the system has a function of decreasing the broadcasting channel detection time.
The nature, utility and principle of the invention will be more clearly understood from the following detailed description and the appended claims when read in conjunction with the accompanying drawings.